question

mrfrodo avatar image
mrfrodo asked

Cerbo GX V3.00 and after update to V3.01, System changes CVL from diyBMS

Hello everyone,

I noticed today with Cerbo version V3.00 that the BMS specifications of the diyBMS (CAN bus - Charge Voltage Limit CVL) are changed by the Cerbo system.

55.2V was set in the diyBMS and after activating the DC coupled PV feed in and limiting to 100/1000W, the CVL value changed to over 58V!!!! The diyBMS then opened the main contactor.

If I switch off the limitation, the CVL slowly falls to the set value of 55.2V.
After a short time the value rises to 55.4V and falls to 55.1V.

After the update to V3.01, the result was the same.

cerbo gx
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mrfrodo avatar image
mrfrodo answered ·

Dear Mr. @mvader (Victron Energy),

please notice my post above.

Thank you.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·

Hi @MrFrodo,

We have to be very clear on this point that Victron offers no support for 3rd party DIY BMS systems.

It is fine to discuss in the modifications space, but please do not ask for help from Victron.

This is documented here on our battery compatibility guide.

cleanshot-2023-09-05-at-193706.jpg


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mrfrodo avatar image mrfrodo Guy Stewart (Victron Community Manager) ♦♦ commented ·

Dear Mr. Stewart,

thank you for fast answering.

When describing my problem, I hoped that people would realize that the problem was not the third party diyBMS, but the programming of the Cerbo GX.

The diyBMS does exactly what it should - and has for a long time.
If there were any problems, I also communicated them in their Github.

Now it's a Victron bug!

Apparently, the activation of the grid feed in, in combination with the power limitation, influences the charging system.
But that's exactly what it shouldn't do!
It must accept the values of the BMS - and it doesn't matter which BMS it is.

Please check this matter internally.

I would be happy to send you a video and provide you with information.

I know that Victron also has battery systems.
Unfortunately, these are about 4500€ more expensive with a comparable capacity.
This is probably why many people rely on other batteries and BMS systems.


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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ mrfrodo commented ·

The behaviour of the battery charging controls when enabling grid feed-in hasn't changed in any recent Venus releases.

It is documented in the GX manual that enabling feed in will override battery limits so that the MPPT will continue to produce energy once the battery target is reached to allow surplus for the export.

There are several systems that cannot accept this over voltage condition, usually due to using an unsupported and untested BMS, and then need to disable feed-in.

There are several posts about this behaviour on the community, but this is good one to start - https://community.victronenergy.com/questions/187320/dvcc-feedin.html

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mrfrodo avatar image mrfrodo Guy Stewart (Victron Community Manager) ♦♦ commented ·

Dear Mr. Stewart,

you wrote:
The behavior of the battery charge control when the grid feed is activated has not changed in the last Venus versions.

I only noticed it yesterday when I wanted to use Grid feed in and power limiting to grid.
If the code is not changed for that, then it was always like that.


You wrote:
It is documented in the GX manual that enabling injection overrides battery limits, so the MPPT will continue to produce power once the battery target is reached to allow surplus for export.


From your GX manual link:
Note: When DC-coupled PV feed-in excess is enabled with ESS, the DVCC system will not apply the DVCC charge current limit from PV to battery. This behaviour is necessary to allow the export. Charge voltage limits will still apply.

Charge voltage limits will still apply!!!
Thats quite better so, incorrect use of these settings could destroy your battery and cause harm!


You wrote:
There are several systems that cannot accept this overvoltage condition, mostly due to using an unsupported and untested BMS, and then must disable the feed.

In my case, the diyBMS shut down cleanly after Cerbo decides to manage voltage on his own and one cell had 3,650V (58,4V pack)
What does your BMS do? At these voltages it still switches off - and thats quite better so.


You wrote:
There are several community posts about this behavior, but this one is a good place to start - https://community.victronenergy.com/questions/187320/dvcc-feedin.html

Yes, for CCL it is right!
But thats not my Problem - My Battery can be charged with 230A!
You have to achieve that first. My three Quattro II then tap enough energy for making AC
But at 55,2V the ohm´s law reduce the Amps to nearly zero.

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